1. Field of the Invention
The present invention relates to improvements in an objective lens driving apparatus provided for an optical information recording and reproducing apparatus or the like which can record, reproduce, or erase information optically by irradiating a recording medium with a light beam.
2. Description of the Background Art
An objective lens driving apparatus which drives an objective lens biaxially to control a position of condensed light of a light beam which irradiates information of a recording medium such as magneto-optical disk or the like through an objective lens in focusing and tracking directions is known.
FIG. 4 is a perspective view of an example of such objective lens driving apparatus.
A lens holder 53 which holds an objective lens 52 is provided for an objective lens driving apparatus 51. At both sides of lens holder 53, elastic bodies 55, 55, . . . which support lens holder 53 movable in two directions against a fixed portion 54 are attached at upper and lower positions, and damper members 56, 56, . . . are adhered to the joint portion in the vicinity of fixed portion 54. Elastic body 55 has a portion fixed to fixed portion 54 and a portion fixed to lens holder 53, which are formed of one linear elastic member. Damper member 56 is affixed in the vicinity of a joint between elastic body 55 and fixed portion 54.
A focusing coil 57 and a tracking coil 58 are adhered to the center hole of lens holder 53. Parts of focusing coil 57 and tracking coil 58 are located in a magnetic gap 59a in a magnetic circuit 59 extended from fixed portion 54, and the magnetic circuit includes permanent magnets 60a, 60b and yoke portions 61a, 61b. Focusing coil 57 is coiled to enclose one of the permanent magnets 60a and yoke 61a, and a portion unnecessary to generate driving force is positioned outside magnetic gap 59a.
In the conventional structure mentioned above, vibrations of movable portion in the focusing and tracking directions are suppressed to some extent by damper members 56.
FIG. 5 is a plan view of a conventional object lens driving apparatus showing a turn of the movable portion around an axis in the focusing direction, and FIG. 6 is a side view of the conventional objective lens driving apparatus showing a turn of the movable portion around an axis in the tracking direction. However, vibrations of elastic body 55 in expanding and contracting directions along the length or a torsional vibration of elastic body 55, which are generated when a turning force around the axis in the focusing direction as represented by an arrow A in FIG. 5 and turning force around the axis in the tracking direction as represented by an arrow B in FIG. 6 are exerted, are hardly suppressed. Therefore, as shown in FIGS. 7A, 7B, 7C and 7D, high resonance peaks 62a, 62b, 62c and 62d remain in transfer function. FIGS. 7A and 7B are graphs showing gain-to-frequency and phase-to-frequency transfer functions in the focusing direction, and FIGS. 7C and 7D are graphs showing gain-to-frequency and phase-to-frequency transfer function in the tracking direction.
A structure of a supporting member to suppress the vibrations mentioned above is disclosed in Japanese Patent Laying-Open No. 63-195834. However, in the structure, a flexible portion (elastic body) curved in the form of arc is used. Therefore, it is necessary to process the elastic body to a complicated shape and manufacture of this shape thereof is difficult. Additionally, since the elastic body has a complicated shape, it is disadvantageous in miniaturizing the apparatus according to a miniaturized, light weighted movable portion.
Furthermore, since the flexible portion is in a small form of a circular arc, it is difficult to obtain a suitable primary resonance frequency for the miniaturized, light weighted movable portion.